Composite material leaf springs are known and typically comprise a filler material, for example glass roving or other filamentary solids, in an organic resin matrix such as thermoplastic or, more typically, thermosetting plastic. Such springs are shown, for example, in U.S. Pat. Nos. 2,600,843, 2,829,881 and 3,142,598. Known methods of making composite material leaf springs include, for example, filament winding, compression molding and pultrusion.
In the past, composite material leaf springs have been used in motor vehicle suspension systems with associated hardware to hold the spring accurately in position. Such spring clamping hardware has been fashioned after hardware previously known for use in conjunction with metal leaf springs. In a typical arrangement, the spring is positioned between a clamping plate on one side and the axle or other wheel carrying member on the other side. Often, a second clamping plate or the like is positioned between the spring and the axle to act as a spring seat. Bolts or the like, for example, U-bolts, are used to clamp the clamping plate and spring to the axle. An abrasion resistant pad can be used between the spring and the axle (or spring seat). Exemplary clamping hardware for a composite material leaf spring is seen, for example, in U.S. Pat. Nos. 3,968,958, 3,586,307 3,541,605.
Known leaf spring clamping hardware has been found inadequate in certain respects for use in conjunction with composite material leaf springs. Specifically, such spring clamping hardware has been found inadequate to hold the spring in a fixed position relative the axle under conditions experienced in ordinary use. More specifically, known spring clamping hardware often has failed to prevent longitudinal movement of the spring, that is, movement of the spring in a direction along its longitudinal axis (which typically is transverse to the longitudinal axis of the axle). Movement of the composite material leaf spring relative the axle or other wheel carrying member in a direction along the longitudinal axis of the leaf spring would change the pivot point of the leaf spring against the axle. Consequently, the spring rate would be altered and the spring would fail to perform according to design. Moreover, upon flexure of the spring, the compressive and tensile stresses would be improperly distributed, which could lead to increased material fatigue and decreased spring life. Moreover, if excessive, such movement could lead to damage to a vehicle powertrain.
While the longitudinal position of the spring could be adequately fixed by providing a hole through the composite material of the leaf spring and bolting the spring to the spring clamping hardware, this presents several disadvantages. Providing the bolt hole in the leaf spring requires additional fabrication time and introduces additional complexity and cost. In addition, the bolt hole significantly weakens the composite material spring and the spring, therefore, must be made larger, heavier and more costly.
A leaf spring clamp suitable for use with a composite material leaf spring is disclosed in above mentioned commonly assigned U.S. Pat. No. 4,519,590. Therein a leaf spring clamp is disclosed to comprise a rigid clamp base which forms a channel to jacket the leaf spring, and a resilient insert which is inserted between the leaf spring and the rigid clamp base. The resilient insert fills substantially entirely the space between the leaf spring and the rigid clamp base. It was found that displacement of the leaf spring within the clamp, especially large bending displacements of the spring, is impeded disadvantageously by the presence of such resilient insert. The resilient insert cannot be eliminated since the leaf spring must be effectively isolated from rigid clamp parts to prevent abrasion and crushing damage to the synthetic material of the spring. In above mentioned commonly assigned U.S. patent application Ser. No. 689,364, a leaf spring clamp is disclosed in which resilient inserts provide voids to accommodate bending displacement of a leaf spring within the clamp.
In the composite leaf spring clamp design disclosed in each of the abovementioned related cases, a degree of pre-load is exerted on the resilient inserts in the assembled clamp. The inserts are placed under a pre-load in part to assure better restraint of longitudinal movement of the spring. According to those designs, U-bolts are employed to hold metal clamp plates a pre-selected distance apart, with the resilient inserts (and leaf spring) sandwiched between them. The torque applied in tightening the U-bolt nuts determines the level of pre-load. This feature has been found to present certain difficulties in achieving consistent pre-loading of the clamps during initial assembly. Also, during re-assembly following repair or service, there is a possibility that the U-bolts could be improperly tightened, resulting in incorrect pre-loading of the clamp. In addition, there is the risk that U-bolt nuts might inadvertently loosen through use over time. It has been found that the degree of pre-load within the clamp effects the performance of the leaf spring. Thus, there is a need for a leaf spring clamp of the subject type in which the correct pre-load can be easily achieved with good repeatability and maintained during use over time.
It is an object of the present invention to provide a leaf spring clamp which secures a leaf spring, especially a filament reinforced composite material leaf spring, in position in a suspension system. More particularly, it is an object of the invention to provide a leaf spring clamp which in ordinary use substantially prevents longitudinal movement of the leaf spring. Furthermore, it is a particular object of the invention to provide a clamp which does not require either damage to or dislocation of either the reinforcing filaments or the resin matrix of the leaf spring and, specifically, which does not require a hole through the leaf spring or concavities in the surface of the leaf spring or other complexities in the shape of the leaf spring.
Additional objects and advantages of the invention will be apparent from the following disclosure.